The present invention relates to appliance control knob assembly constructions, and particularly to constructions of control knobs for use in laundry appliances, such as automated laundry washing machines and dryers.
Automated laundry appliances (such as laundry washing machines and dryers) typically include an external generally rectangular cabinet, a control panel for controlling the washer/dryer operation, and a hinged lid or door that may be swung open to provide top or front-load access to a rotatable cylindrical wash basin (in the case of a washer). In use of an automated laundry washing machine, after placing a load of laundry in the wash basin, along with a suitable type and quantity of laundry detergent, a wash process is initiated by an operator through interaction with the control knob. Similarly, with a dryer, a wash load drying process is initiated through interaction with a control knob. The control knob provides a user interface through which a user may make selections of cycles and various wash (or dry) control parameters. Controlled operation sequences may be carried out using an electronic controller that may, e.g., be provided as an integral part of the control panel, or mounted separately and suitably connected therewith. Such a controller may comprise one or more suitably programmed microprocessors or application specific integrated circuits (ASICs), operably connected to suitable circuitry, e.g., for driving the wash basin drive motor, actuating operation components (e.g., valves and a pump) to fill the wash basin and drain it, dispense additives, etc. Such operations will be carried out in accordance with commands of the controller, generated on the basis of program control and possibly also signals received from various sensors monitoring various operation-related parameters.
Many current designs for knobs in washer and dryer consoles comprise a knob shell with a concentric knob shaft on the inside that is supported on its outside diameter by either a cone shape that contacts the knob shaft only over a very small area close to the front face of the knob, or a cylindrical shape that holds the knob shaft over a larger area/length of the knob shaft.
The rearward end of the knob shaft often is supported by an encoder on an electronic circuit board. Alternatively, some knobs are supported only by an encoder. These designs can create problems of displacement of the knob from its intended aligned mounting position and friction between the knob shaft and the supporting geometry. Unwanted lateral movement of the knob may result from the gap necessarily provided between the knob shaft and the shaft support geometry to allow low friction rotation of the knob. This lateral movement may result in undesirable loosening of the knob or misalignment in relation to the encoder that may hinder knob operation. It may also provide an undesirable user feel. As that gap is increased, the lateral movement may allow the outermost diameter of the knob to rub on the surrounding console structure, causing more friction and wear. This issue is even more prevalent on designs where the knob is supported by only the encoder, as there is a much higher moment arm for any lateral forces (including gravity) to affect the position of the knob and allow it to rub on the console. Conversely, as the gap between the knob shaft and its support geometry is narrowed to reduce lateral knob movement, friction between the knob shaft and its support geometry may increase.
Axial movement of, or forces on, the knob also may be a problem. As the knob is pushed inward during use, it may frictionally engage against the knob shaft support geometry leading to undesirable increased rotation resistance. Axially directed forces on and/or movement of the knob can also cause damage to the encoder to which the knob shaft is attached. If the knob is pulled outward from the console during use, there also may be increased friction between the knob shaft and its support geometry. Also, there may be increased friction between the knob and the console. Small dimensional variations on any of the interacting parts, which are to be expected in injection molding processes, can have a great impact on any of these three potential issues.